added VGlue to cover the case where we can't precompute the glue

testsuite/compiler/compute/predef.gfs

@@ -32,4 +32,5 @@ cc "x"++SOFT_SPACE++"y"
 cc "x"++CAPIT++"y"
 cc "x"++ALL_CAPIT++"y"
 cc "a"+"b"
+cc <\x->x+"b" : Str -> Str>
 cc eqInt (length ("a"+"b")) 2

testsuite/compiler/compute/predef.gfs.gold

@@ -31,4 +31,5 @@ user error
 "x" ++ Predef.CAPIT ++ "y"
 "x" ++ Predef.ALL_CAPIT ++ "y"
 "ab"
+\v0 -> v0 + "b"
 Predef.PTrue